1. Technical Field
The present invention relates to an electronic apparatus including a functional element such as a resonator, a sensor or an actuator, and a manufacturing method thereof. Furthermore, the invention relates to an oscillator, an electronic appliance, a mobile unit and the like that use such an electronic apparatus.
2. Related Art
For example, in an electronic apparatus including a capacitive type resonator as a functional element such as a MEMS (Micro Electro Mechanical Systems) device, the resonator is hermetically sealed in a vacuum state or with an inert gas contained within a hermetically sealed structure. Even in an electronic apparatus that does not require a vacuum state or the like, in order to prevent the influence of dust, moisture and the like, the functional element is hermetically sealed within the hermetically sealed structure.
In order to form a hermetically sealed structure in such an electronic apparatus, for example, a sacrificial layer is formed within a cavity where the functional element is provided, the cavity is covered with a cover portion having release holes formed therein, and thereafter the sacrificial layer is removed by release etching. Furthermore, a sealing layer for sealing the release holes or the like is formed on the cover portion.
However, the cover portion is easily deformed during the step of forming the sealing layer or the like on the cover portion. Accordingly, the cover portion needs to be thick in order to increase the strength. It is therefore not possible to form micro release holes in the cover portion, and thus the release holes have a large diameter. As a result, the sealing layer for sealing the release holes also becomes thick, and therefore it has been difficult to miniaturize the electronic apparatus.
As a related technique, JP-A-2014-192435 (paragraphs [0008], [0027] and [0036], FIG. 1) discloses, in FIG. 1, an electronic apparatus including a substrate 10, an underlying layer 20 that is formed on the substrate 10 and has an opening 22, a functional element 30 that is provided on the underlying layer 20, a surrounding wall 40 that forms a hollow 1 for housing the functional element 30, at least a portion of the surrounding wall 40 being disposed within the opening 22, and a cover member 50 that is disposed above the surrounding wall 40 and covers the hollow 1.
The cover member 50 is composed of a first sealing layer 54 having a through hole 52 and a second sealing layer 56 that is stacked on the first sealing layer 54 and seals the through hole 52. If the thickness of the first sealing layer 54 is increased so as to secure the strength, the diameter of the through hole 52 needs to be increased in order to form the through hole 52. This requires the thickness of the second sealing layer 56 for sealing the through hole 52 to be increased, which hampers miniaturization of the electronic apparatus.